This invention relates generally to aerial ladders and more particularly to a mechanical linkage which allows a multiple section aerial ladder to be controlled from both its base end and its top or working end.
Truck mounted aerial ladders are useful in a variety of applications such as performing work on billboards and other outdoor signs and other elevated devices. The aerial ladder is typically mounted in the bed of a truck on a turret which permits the ladder to be varied in its rotational position. The ladder can also be pivoted up and down to control the elevation of its top or working end. The type of aerial ladder to which the present invention pertains includes multiple sections which can be extended and retracted relative to one another to vary the overall length of the ladder. Hydraulic motors and cylinders are provided to rotate, elevate and extend the aerial ladder under the control of hydraulic valves that are actuated by hand levers.
It is desirable to provide the ladder with one set of controls at its base end and with another set of controls at its top end. This permits the ladder to be controlled from the ground and also by a worker stationed on the top end of the ladder. Often, the working end of the ladder is equipped with a bucket or basket which carries a worker, and work can be carried out safely and expeditiously if the worker is able to start and stop and control the ladder from his station in the basket.
U.S. Pat. No. 3,360,076 to Stilwell; U.S. Pat. No. 3,489,243 to Prescott et al and U.S. Pat. No. 3,196,979 to Garnett disclose the telescoping aerial booms which have controls located on the top of the boom where they can be manipulated by a worker carried in the basket. In the case of a telescoping boom, the control rods can easily extend within the hollow boom and there are no severe space limitations. However, in the case of an aerial ladder, it is necessary to avoid obstructing the working area of the ladder with control linkages and the like, and it is much more difficult to provide a control linkage which extends the entire length of the ladder without hindering extension and retraction of the ladder sections. To my knowledge, there have been no successful insulated mechanical control systems developed for aerial ladders which permit all functions of the ladder to be controlled from both the top and base ends of the ladder.
It is the primary object of the present invention to provide, in a multiple extending section aerial ladder, an insulated mechanical control linkage which permits all functions of the ladder to be controlled from both the base end and from the elevted working end of the ladder.
Another object of the invention is to provide a control linkage of the character described which is installed at an unobtrusive location on the ladder. The components of the linkage system are mounted between the sides of the three ladder sections where they can properly interact with one another without obstructing the working area of the ladder.
Yet another object of the invention is to provide control linkage of the character described in which each ladder function has one control lever at the base end of the ladder and another control lever on the working end of the ladder. It is a significant feature of the invention that the control levers in each pair are moved in the same direction (up or down) in order to effect the same direction of ladder movement. The linkage between each pair of levers includes a reversal mechanism which compensates for the differences between the direct acting upper levers and the beam type lower levers.
A further object of the invention is to provide a linkage of the character described which presents only nonconducting materials in the vicinity of the ladder tip. Electrically conducting materials are insulated at the ladder tip so that work near power lines and other electrical devices can be carried out safely.
An additional object of the invention is to provide a linkage of the character described which is simple and economical to construct and install and which functions in a safe and reliable manner.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.